The problem is not the Roboduino, but the servo library. It was made so it uses only pins 9 and 10. For more servos, you need to install the SoftwareServo library, that works the same, but with all Roboduino pins. So, after you download and install the SoftwareServo library, you can use the same code, but instead of including Servo library, you include SoftwareServo library. Also, the servos need a refresh command that you need to call any time between 10 and 30 ms. Below is the sample code and I have attached the library:

void loop() { val = analogRead(potpin); // reads the value of the potentiometer (value between 0 and 1023) val = map(val, 0, 1023, 0, 179); // scale it to use it with the servo (value between 0 and 180) myservo.write(val); // sets the servo position according to the scaled value delay(15); // waits for the servo to get there